Copperhead dwarves have a reputation for being much more friendly to humans and trolls than the more conservative clans mining below Uberwald (the Deep-Downers), having had to deal with humans from Lancre in trade for many years, and Ankh Morpork more recently. In Copperhead you can find excellent dwarf thudmeisters (masters of the game Thud), which surely also contributes to the open attitude of the Copperhead Dwarves.